Thin films of ZnS with thicknesses ranging from 100 to 600 nm have been deposited on glass substrates by close spaced thermal evaporation. All the films were grown at the same deposition conditions except the deposition time. The effect of thickness on the physical properties of ZnS films has been studied. The experimental results indicated that the thickness affects the structure, lattice strain, surface morphology and optoelectronic properties of ZnS films significantly. The films deposited at a thickness of 100 nm showed hexagonal structure whereas films of thickness 300 nm or more showed cubic structure. However, coexistence of both cubic and hexagonal structures was observed in the films of 200 nm thickness. The surface roughness of the films showed an increasing trend at higher thicknesses of the films. A blue-shift in the energy band gap along with an intense UV emission band was observed with the decrease of film thickness, which are ascribed to the quantum confinement effect. The behaviour of optical constants such as refractive index and extinction coefficient were analysed. The variation of refractive index and extinction coefficient with thickness was explained on the basis of the contribution from the packing density of the layers. The electrical resistivity as well as the activation energy were evaluated and found to decrease with the increase of film thickness. The thickness had a significant influence on the optical band gap as well as the luminescence intensity.

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Indium sulfide (In2S3) layers were deposited on glass substrates by close-spaced evaporation of In2S3 powder at various deposition temperatures in the range 200–350 °C. The chemical composition, structure, surface morphology, optical and electrical studies were carried out using appropriate techniques. The chemical composition of the layers analysed using x-ray photoelectron spectroscopy studies revealed that the layers prepared at a substrate temperature of 300 °C were sulfur deficient. These layers exhibited a broad (1 0 3) orientation, corresponding to the tetragonal structure of In2S3 with an average grain size of 32 nm and an average surface roughness of 1.4 nm. The layers showed a combination of tetragonal and cubic structures at lower substrate temperatures (⩽300 °C) without the presence of other phases of In2S3. The layers had a high optical transmittance of 78% and the energy band gap of the films increased from 2.09 to 2.52 eV with the increase in substrate temperature. The films grown at 300 °C showed a conductivity of 7.81 × 10−4 (Ω cm)−1. The Arrhenius plots indicated two regions where the carrier transport was mainly due to thermionic emission in the temperature region 290–450 K while Mott's hopping was predominant below 290 K.

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